Method of and means for controlling the viscosity of extruded plastic ribbons



JUL 18 1944. J. BAILEY l-:rAL

METHOD 0F AND MEANS FOR CONTROLLING THE VISCOSITY OF EXTRUDED PLASTICRIBBONS Filed Nay 13, 1942 Patented Jan. 18, 1944 .unrnop oEAND MEANSFOR con'rnoLLINd THE viscosrrY or EXTRUDED `PnAs'ric RIBoNs ames Bailey,West Hartford, and Raymond S. Jesionowski, Hartford,Conn., assignors toPlax Corporation, Hartford, Conn., a. corporation of DelawareApplication May 13,1942, serial 110,442,845; `(ci. `lat-1,2)

11 Claims.

The present invention relates to dry process extrusion of an organicplastic sheet or ribbon; the term dry process meaning that the plasticcompound which is extruded is solvent-free or free of solvents of thevolatile type, such as acetone or alcohol. j

The process and apparatus for dry process extrusion for organic plasticsheet orribbon are fully described in the copending application of JamesBailey, Serial No. 423,912 filed December 22, 1941, and which onSeptember 29, .1942, issued as United States Patent No. 2,297,645. Astherein pointed out, upon the ribbon leaving the extrusion nozzle, it isnecessary to control the viscosity thereof as the ribbon is transverselystretched, as well as to protect the ribbon from chilling drafts whichwill deform or injureit, and to accomplish the foregoing withoutmarringthe surface thereof.

More specifically, the object of the present invention is to provide animproved method `and apparatus for accomplishing the aforestatedv pur-Another object isto provide improved'means for controlling the viscosityof the extruded rib- -L bon as it leaves the extrusion nozzle bysubjecting the same to heat and `wherein the degree of heat applied toany portion of theribbon may be accurately controlled.

Another object is to provide means for controlling the viscosity of ,theribbon by applying heat thereto and wherein the heat is so applied thatit will be evenly distributed and diffused to prevent line scorching orexcessive 'heating and stretching of a longitudinal portion of theribbon. A still further object is to provide heating means of extremelysimple construction wherein the various parts thereof may be readilyandfeconomically replaced and rapidly and readily renewed orinterchanged.

Other objects will be in part obvious and in part pointed out more indetail hereinafter.

The invention accordingly consistsin the features of construction,combination of elements,

Fig. 2 is a vertical sectional elevation ofthe construction shownin Fig.1;

Fig. @isa view of a modied form of burner-for theheating means; and

Fig. 4 is a View of .anotherheating means embodying the inventionherein. v

Referringto ,the drawing, the plastic material afterrpreparatoryconditioning ejnterswthe nozzle N kand is extruded through theextrusion' slot lll defined by topand ,bottom adjustable lips I2 andI-Il in to a -continuousjsheet or ribbon R, Upon leaving the nozzle,vthe edges of the ribbon are 'immediately gripped by gripping means vvGydagrammatically shown in Figs. I1 and 2; the

rst series of gripping means also functioning to chill the sheet orribbon edges tol provide hardened edge portions between which the bodypart of the vribbon is 'thereafter supported. In addition to supportingthe ribbon,y the gripping means are'arranged in paths diverging fromthe" nozzle tol-,thereby subjecttherihbon to transverse'tensionandstretch it to a desired width; Prefer-` ably, the ribbon `is' alsovsubjected to Ylongitudinal tension, partly .by thegripping meansG andby V.suitable pulling rifleams-,` suchas shown in said Patent No.2.2973345, ,engaging a cool portion of the ribbon. v Y p In order tocontrol the viscosity ofthe ribbon during these initial operations;-there is located adjacent the nozzle N` heating means H; these.

means being' horizontally positioned beneath and out of 'contact withthe ribbon R. More specifically, the heating means comprisesfa plurality of transversely spaced, longitudinally extending heating elementsi8; leach,elementin the embodiment shown Vbeing a gas burner. Eachburner 'is relatively ,long Yand isfclosed atthe end adjacent ,thenozzleand at the other end `connects to a, -rser 20 extending from la`main gasmain 22. As best ,seen'inFigs 2 and3',e `ach 4 riser 20 hasarranged therein a controlvalvefM and arrangement of parts which will beexemplitails of construction and diagrammatically showing the extrusionand. ribbon supporting means;

whereby the vflow of gas therethrough may be accurately Acontrolled tothus vary the'heat created .by each burner and toppermlt control ofanyelement individually of any other element.

In orderto more evenly distribute the heat and likewise prevent linescorching or -excessive heating. of a. longitudinal portion ofthegribbon, each element I8 extends longitudlnallyof the pathof 'travelof the ribbon'R in a. zigzag o r serpentine path. 'Ifo accomplish this,each-.element may consist of a plurality of sections 325,'

Aeach `section being connected` to the'next succeeding section vby anglefittings -28 of approxi- -mately and each successivetting being reversedrelative to the preceding tting. The heating elements l-are positionedwell below the ribbon R and located within a frame 30 having side wallsdiverging outwardly fromthe nozzle in like manner to the gripping means,and it will be noted that to compensatefor the narrower section adjacentthe nozzle the side heating elements I8 are' somewhat shorter than thosein the center. As a result of this arrangement, the

ribbon is heated along approximately longitudi` nal elongated zonesarranged transversely of the ribbon, and the heat from each element isdirected towards a respective longitudinal zone along lines at angles tothe direction of travel ofthe ribbon so that various portions of theribstrips 32 is a diffusing bed B comprising a substantial layer ofpulverulent ceramic or other heat resisting granular material 34enclosed with- `lin a close-mesh'screening 36. In thisway it will 'y beseen that the heat created by the burners will v,circulateupwardlythrough the spacings 33 beincreased. In other words, the heating in theseveral zones would be selectively lregulated in accordance withvariations in resistance of the portions of the ribbon to stretch. Inaddition to variations in thickness as the1ibbon leaves the nozzle,there also may be a variation in temperature or temperature gradientacross the ribbon due to a temperature drop across the nozzle. This dropmay approximate ll' F. and must be compensated for in order to have thefinished product of uniform thickness.

Likewise, aspreviously explained, upon the ribbon leaving the nozzle itis immediately en gaged by gripping rolls which chill the edges thereof,and to prevent this chill from extending inwardly of the edges of theribbon, the heating elements I8 adjacent the side edges may `be adjustedto create more heat than those at the center of the ribbon. This heatingof the sheet adjacent the side edges also prevents riillng of the sheetvinwardly of the chilled edges by permitting plastic now thereof` underthe transverse tensioning. If it'is also desired to control thelonigtudinal heating effect of the elements I8, each ofthe fittings 28may also be provided with a control valve as shown in Fig. 3.

It will be seen that Iby spacing the elements I8 tween the metal stripsl32 to heat the bed B 1 Awhich directlyV underlies -the ribbon R, wherebyVthe ribbon will be heated by radiant heat, and all direct impingementof` th'eames on the ribbon is prevented.

In order to'protectthat portion of the rib- -bon immediately adjacentthe nozzle from chilling drafts, the frame 30'further supports a bafile38 arranged intermediate the ends of the ele ments' I8 and the nozzle Nthis'b'ale cooperating *with the heating means to protect the sheet or fribbon throughout the zone of transverse stretching and the heatingmeans'protecting it Vfor a distance therebeyond.

With the foregoing arrangement ity will be seen that the viscosity ofthe ribbon RA upon its leaving the nozzle may be accurately controlledby controlling the heat created by the heating meansy This is necessaryfor various reasons. For example, it will be appreciated that because ofthe size of the nozzle N and the extremely small opening of the nozzleslot it is difcult'at times to accurately set the nozzle 'slot so --thatthe extruded ribbon 'will be of equal thickness throughout its width. Ifan accurate setting is not made and the extruded ribbon is of' greaterthickness at one side thanat the other, then, if the thicker 'portionshould Ibe cooler and therefore more viscous than the thinner portion,more heat may be applied by increasing the ames of theb'urnersl to thethick side of the ribbon `by manipulation of the necessary individualburnercontrol valves 24, thus causing the plastic of this portion of theribbon to flow and stretch more than the thinnerpor- .tion of the ribbonduring the transverse tensionin'g, whereby the thickness of the finishedsheet may be made uniform. v,On the other hand, the thinner portion maybe4 cooler andtherefore have more, resistance to stretching than thethicker portion, in which casethe heat in the zone or zones of thethinner yportion wouldV be` .transversely of the ribbon each element orgroups of adjacent elements in effect provides an independentlongitudinal heating zone whereby the temperature of the bed Bimmediately above same may be raised or lowered lby increasing the heatproduced by the element or groups thereof. As a result, the ribbon R inelect passes over a plurality of heating zones, all of which may beadjusted to produce the same temperature,

or each one of which may be adjusted to produce a higher or lowertemperaturefas desired, to control the temperature or maintain thedesired temperature gradient transversely of the ribbon particularlywhere it is being stretched transversely.

Referring now to the embodiment illustrated in Fig. 4, theheatingelements I8 are similar to those shown in Figs. 1 and 2. However,in this 44 may each be made of one piece, thus facilitating the assemblyand interchangeability of the parts.

As many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying .drawingshall be interpreted as illustrative and i not in a limiting sense.

It is also to be understood that the language used in thefollowingclaims is intended to cover all of the generic and specific features ofthe invention herein described and all statements of the scope of theinvention which as a matter of language, might be said to falltherebetween.

We claim as our invention:

l. The method of forming a sheet of solventfree organic thermoplasticmaterial which comprises continuously extruding the material through anozzle to torni a flat ribbon, gripping the edges of said ribbon nearsaid nozzle and for a substantial distance' beyond said nozzle andstretching the ribbon transversely to widen it and reduceits thickness,applying heat to said ribbon as it is being stretched from transverselylarranged approximately longitudinally elongated duce its thickness,applying heat to said ribbon from transversely arranged approximatelylongitudinally elongated zones, diiusing said heat to prevent excessivelocalized heating of the ribbon, and selectively regulating the heatfrom said zones in accordance with transverse variations in temperaturesand viscosity of the'ribbon to cause said ribbon to stretch into a.sheet of uniform thickness.

3. The method of forming a sheet of organic solvent-free thermoplasticmaterial which comprises continuously extruding the material in aviscous state through a nozzle to form a fiat ribbon, gripping the edgesof the ribbon near the nozzle and for a substantial distance beyond saidnozzle and transversely stretching the ribbon to widen it and reduce itsthickness, applying heat to the ribbon to control its temperature andviscosity for stretching from transversely arranged approximatelylongitudinally elongated zones, and directing the heat from each zonetowards the ribbon along successive lines `disposed at angles to thelongitudinal direction of travely of the ribbon so that the variousportions of the ribbon in each zone are intermittently heated andexcessive heating and stretching of the ribbon along localizedlongitudinal lines are prevented. f

4. The method oi forming a sheet of'solventfree thermoplastic materialwhich comprises continuously extruding the material in a viscous statethrough a nozzle to form a fiat ribbon, gripping the edges of saidribbon near said nozzle and for a substantial distance beyond saidnozzle and transversely stretching the ribbon to Widen it and reduce itsthickness, applying heat to said ribbon to control its temperature andviscosity for stretching from transversely arranged approximatelylongitudinally elongated zones, directing the heat from each zonetowards the ribbon along lines at angles to thedirection of travel ofthe ribbon to prevent excessive heating and stretching of the ribbonalong localized longi-A tudinal lines, and selectively regulating theheating from said zones in accordance with the transverse variations intemperature and viscosity of the ribbon to cause said ribbon to stretchinto a sheet of uniform thickness.

5. Means for forming a sheet oi solvent-free organic thermoplasticmaterial comprising a nozzle through which the plastic is extruded in aviscous state to form a flat ribbon, means for gripping the edges of theribbon near the nozzle and for a substantial distance beyond said nozzleand stretching it transversely to Widen it and reduce its thickness,heating means disposed beneath` said sheet and approximatelyco-extenslve with the area in which it is stretched and arranged to heatsaid ribbon from transversely arranged approximately llongitudinallyelongated zones, and means for regulating the heating means in saidzones so as to maintain a temperature gradientV transversely of saidribbon in accordance with the variations in temperature and viscosity inthe sheet.

6. Means for forming a sheet of solvent-free organic thermoplasticmaterial comprising a nozzle through which the material is extruded in aviscous state to form a nat ribbon, means for gripping the edges of saidribbon and stretching it transversely to widen it and reduce itsthickness, means for applying heat to said ribbon from `transverselyarranged approximately longitudinally elongated zones, meansbetween'said heating means and ribbon for diffusing the heat to preventexcessive localized heating of the rib bon, and means for selectivelyregulating the heating means in the several zones in accordance withtransverse variations in temperature and viscosity of the ribbon tocause said ribbon to stretch into a sheet of uniform thickness.

'7. Means for forming a sheet of solvent-free organic thermoplasticmaterial comprising xa nozzle through which the plastic is extruded in aviscous state to form a flat ribbon, means for gripping the edges ofsaid ribbon near the nozzle and for a ,substantial distance beyond saidnozzle and transversely stretching the ribbon to widen it and reduce itsthickness, means for applying heat to said ribbon from transverselyarranged approximately longitudinally elongatedv zones and alongsuccessive lines in each zone at angles to the direction of travel ofthe ribbon so as to control its temperature and viscosity for stretchingwithout excessively' heating and stretching the ribbon along localizedlongitudinal lines.

8. Means for forming a sheet of solvent-free organic thermoplasticmaterial comprising a nozzle through which the material is extruded in aviscous state to form a 'at ribbon, means for gripping the edges of theribbon and stretching it transversclypto widen it and reduce itsthickness, heating means disposed beneath said ribbon approximatelyco-extensive with the area in which it is stretched, said heating meanscomprising a plurality of transversely spaced gener-r allylongitudinally extending heating elements, and means for selectivelyregulating said heating elements so as to maintain a temperaturegradient transversely of the sheet in accordance with variations intemperature and viscosityv thereof.

9. Means for forming a sheet of solvent-free organic thermoplasticmaterial comprising a nozzle through which the material is extruded in aviscous state to form a at ribbon, means for` gripping the edges of theribbon and stretching it transversely to widen it and reduce itsthickness, heating means disposed beneath said ribbon approximatelyco-extensive with the area in which it is stretched. said heating meanscomprising a plurality of transversely spaced generally longitudinallyextending heating elements,

means positioned between said heating means and the ribbon for diffusingthe heat created by said elements and thereby yprevent excessive heatingand stretching of the ribbon along localized longitudinal lines, andmeans for selectively regulating said heating elements so as to maintaina temperature gradient transversely of the sheet in accordance withvariations in viscosity thereof.

10. Means ior fori-ning yasheet of .solventf-Vfree organicthermoplasticmaterial comprising a nozzie :through-which the material isextruded in `a viscousstate to form ,u nat ribbon. means for grippingthe edges of the ribbon land.stretcliing it transversely vte widenit andreduce its thicknessyand kheating?inea-ns .disposed Vheneatl'l saidribbon approximately .co-extensive with the Aarea in which lit isstretched, said heating means comprising@ plurality o f transverselyspaceldllongitudi-nally extending heating elements, o-f zigfzag form .sothat the heat from the elements `is directedfjalong zig-zag paths intransversely arranged longitudinally extending zones.

ll. 1-Means ier forming a sheet of solvent-free ,organic thermoplasticmaterial comprising a nozzie through which the material is extruded in alviscous state to form a fiat ribbon,`means for gripping the edges of`the ribbon and stretch-ing it transversely to widen it and reduce itsthickness, heating means disposed beneath said rib-

